One problem related to transmission gear slipping has been reported for the 2004 GMC Envoy. The most recently reported issues are listed below.
We complained about the transmission slipping at 33,000 miles and take it back to the dealer they say the checked the problem and replaced an electrical component, at 50k while my wife was driving on the highway at 65mph lost the power train. After much discussion and three weeks the dealer finally agreed to fix for 500 vice 3300 which they wanted. A week later the transmission is slipping again and now we lost power steering and the gas needle stopped working. I have left messages for the service manager at wiesner GMC in conroe TX and they have not returned any calls. I am now taking the vehicle to a different mechanic to tried to get it repaired.